- Combine the Peanut Dipping Sauce ingredients. Mix briefly (it won't come together), then microwave for 30 seconds. Mix again until smooth. Set aside to cool. Adjust sour with vinegar, salt with salt and spiciness to taste. Thickness can be adjusted with milk or water once cooled.
- Place vermicelli noodles in a bowl and cover with warm water for 2 minutes, then drain (or follow packet instructions).
- Peel the prawns, slice in half lengthwise and devein.
- Remove the crunchy core of the lettuce leaves.
- Place some vermicelli noodles and bean sprouts in a lettuce leaf, then roll it up, finishing seam side down. Repeat.
- Fill a large bowl with warm water. The bowl doesn't need to be large enough to fit the whole rice paper in one go.
- Place two rice papers together (if using 2). Note which side is the smooth side - this is supposed to be the outside of the spring roll. Submerge the rice papers into the water (both of them at the same time, together) for 2 seconds. If your bowl isn't large enough to fit the whole rice paper in one go, just rotate it and count 2 seconds for each section you submerge into the water.
- Place both the rice papers (one on top of the other, they will stick together) on a board or the counter with the smooth side down.
- On the top part of the rice paper, place 3 prawns with a mint leaf in between.
- Place the lettuce bundle with the seam side down onto the middle of the rice paper.
- Fold the left and right edges of the rice paper in, then starting from the bottom, roll up to cover the lettuce bundle. Then keep rolling firmly. The rice paper is sticky, it will seal itself.
- Serve immediately with the peanut dipping sauce.